1. Field of the Invention
The present invention relates in general to a rotary head drum device equipped in a video cassette recorder or an integrated system of camera/video cassette recorder, and more particularly to a rotary transformer assembly of such a rotary head drum device which is provided with a shielding wall for preventing leakage of electromotive force between adjacent pairs of channels, thereby preventing generation of cross torque therebetween and, in this respect, providing a stable video signal transfer without generation of noise.
2. Description of the Prior Art
With reference to FIG. 1 showing an elevational sectioned construction of a known rotary head drum device for a video cassette recorder, the known head drum device generally comprises an upper rotary drum 4, which is mounted on a rotating flange 3 fixed to a rotating shaft 2 of a drum drive motor 1. In addition, under the upper rotary drum 4 a predetermined number, for example, 2 or 4, of heads 5 are mounted so as to be circumferentially disposed at the side surface of the drum device and spaced apart from each other at a predetermined angle. A transformer rotor 10 is fixed to the under surface of the flange 3 of the rotating shaft 2, while both a leg relay 6 and a disk relay 7 are mounted on the upper rotary drum 4 so as to cause the video signals to be transferred between the heads 5 and the transformer rotor 10. On the other hand, at a position downwardly spaced apart from the upper rotary drum 4 by a predetermined distance, a lower stationary drum 8 is arranged. The drum drive motor 1 is disposed at a position under the lower stationary drum 8, while a transformer stator 20 is fixedly disposed on the lower stationary drum 8 so as to face to the transformer rotor 10 with a minute space formed therebetween. In result, the video signals are transferred between the upper rotary drum 4 and the lower stationary drum 8. Conventionally, the transformer stator 20 is also electrically connected to a recording/playback signal processing circuit (not shown) by means of a signal transferring cable 9.
Here, the aforementioned transformer rotor 10 and the transformer stator 20 face to each other and constitute a rotary transformer assembly as shown in FIG. 2. Referring to this drawing, the transformer rotor 10 (hereinafter, referred to simply as "the rotor") and the transformer stator 20 (hereinafter, referred to simply as "the stator") are disposed so as to be spaced apart from each other with a predetermined space formed therebetween and each has a plurality of channels 11 or 21 which form a plurality of concentric circular slots as shown in FIG. 3. On the bottoms of the channels 11 and 21, coils 12 or 22 are arranged, respectively. Here, the one group of channels, for example, the channels 11 of the rotor 10 (hereinafter, referred to simply as "the rotor channels"), are formed so as to face to the other group of channels, for example, the channels 22 of the stator 20 (hereinafter, referred to simply as "the stator channels"). Therefore, a magnetic field is induced between each pair of channels, comprising a rotor channel 11 and a stator channel 21 which are facing to each other, by virtue of the coils 12 and 22 thereof and this permits a video signal to be transferred between this pair of channels 11 and 21.
The operation of the known rotary head drum device having the aforementioned construction will be described as follows.
In the case of recording or playback mode of the video cassette recorder, the upper rotary drum 4 of the rotary head drum device is rotated by the driving force of the drum drive motor 1 and this causes the heads 5 disposed at the circumferential surface of the rotary head drum 4 to play back the video signals recorded on the video tape or to record the video signals on the video tape as they revolve under the condition that they come into close contact with the video tape.
Here, the signal transfer between the upper rotary drum 4 and the lower stationary drum 8 is carried out by the rotary transformer assembly in which the coils 12 and 22, each arranged on the bottom of its corresponding channel 11 or 21, cause a magnetic field to be induced between the transformer rotor 10, which rotates together with the rotating flange 3, and the transformer stator 20, which is fixed to the lower stationary drum 8, thereby permitting the video signals to be transferred between the transformer rotor 10 and the transformer stator 20.
That is, when the electric currents in the coils 12 and 22 inside the channels 11 and 21, these channels 11 and 21 facing to each other, vary in their values, the magnetic fluxes across the sectioned areas of the coils 12 and 21 vary, thereby causing an electromotive force to be electromagnetically induced between the coils 12 and 22 due to a potential difference therebetween. Here, in order to cause the electromotive force induced between the coils 12 and 22 to make the electricity be transferred from a coil 12 or 22 of high electric potential to the other coil 22 or 12 of low electric potential, it is necessary to dispose the transformer rotor 10 and the transformer stator 20 so as to closely face each other so that the electromotive force makes the electricity be transferred from the coil 12 or 22 of high electric potential to the other coil 22 or 12 of low electric potential.
However, in such a known rotary transformer assembly of the rotary head drum device, the transformer rotor 10 and the transformer stator 20 are disposed so as to closely face to each other as described above so that the known transformer assembly provides a minute gap, through which the electromotive force induced between the coils 12 and 22 in a pair of channels 11 and 21, which are faced to each other, leaks out, to another pairs of channels 11 and 21 which are adjacent to the pair of channels 11 and 21. Thus, the adjacent pairs of channels 11 and 21 are conventionally affected by the leaked electromotive force and this causes a cross torque to be generated in the adjacent pairs of channels 11 and 21, thereby introducing noise in the video signal.
In an effort to solve the generation of such a cross torque, it has been proposed to widen the interval between the adjacent pairs of channels or to apply at least one short ring to the rotary transformer assembly.
However, to widen the interval between the adjacent pairs of channels 11 and 21 of the rotary transformer assembly detrimentally affects the whole size of the rotary head drum device and, in this respects, impairs the compactness of the final products, such as video cassette recorders, equipped with such a rotary head drum device. As a result, there is a restriction in the widening the interval between the adjacent pairs of channels 11 and 21 so that it is impossible to efficiently prevent the generation of the cross torque caused by the electromotive force which leaks out between the adjacent pairs of channels 11 and 21.
On the other hand, in order to apply the short ring to the known rotary transformer assembly, a conductive short ring 25 may be additionally arranged between adjacent stator channels 21 formed in the transformer stator 20, as depicted in FIG. 3. This short ring 25 is adapted to prevent the electromotive force from leaking out between the adjacent pairs of channels 11 and 21 and, in this respect, to prevent the generation of cross torque caused by the leaked electromotive force. Here, it is noted that the short ring 25 may be arranged at the transformer rotor 10 instead of the aforementioned transformer stator 20. This short ring 25 is conventionally made of a conductive material, such as a copper wire, which can receive the electromotive force. At this time, it may be considered that it is more efficient when a short ring 25 is arranged at each interval between adjacent pairs of channels 11 and 21 , however, in this case, each interval between adjacent pairs of channels 11 and 21 of the rotary transformer assembly is inevitably widened. Therefore, one or two short rings 25 are conventionally arranged in the known rotary transformer assembly.
The short ring 25 disposed at the interval between the adjacent pairs of channels 11 and 21 additionally functions as an earthing ring by which the electromotive force, which wants to leak out from a pair of channels 11 and 21 of the adjacent pairs toward the other pair of channels 11 and 21 of the adjacent pairs, is absorbed before it affects the other pair of channels 11 and 21. Thus, this short ring 25 prevents the generation of the cross torque which is caused by the leaked electromotive force and causes noise in the video signal.
However, in applying the short ring 25 to the rotary transformer assembly, the short ring 25 inevitably occupies an area of the rotary transformer assembly so that it is impossible to provide the short ring 25 for each interval between each two adjacent pairs of channels 11 and 21 as mentioned above. Hence, this type of known rotary transformer assembly has a disadvantage in that applying of the short ring 25 can not prevent all of the leakage of the electromotive force, each occurring between each adjacent pairs of channels 11 and 21. Furthermore, this short ring 25 detrimentally affects the adjacent pairs of channels 11 and 21, between which the short ring 25 is arranged, due to its function as the earthing ring which can absorb the electromotive force as aforementioned, thus weakening the signal intensity. In addition, even though this short ring 25 is intended to prevent the electromotive force from leaking out between the adjacent pairs of channels 11 and 21 by virtue of its function as the earthing ring which can absorb the leaked electromotive force, but it does not practically exhibit excellent results in preventing the leakage of the electromotive force.